The present invention relates to a computer system including a storage system to which a storage virtualizing technique is applied.
Recently, there has been broadly installed a computer system in which one or more external storage apparatuses are connected to one or more host computers or hosts via a Storage Area Network (SAN) such that the hosts use or share a large-capacity storage apparatus including the external storage apparatuses. Such computer system is advantageous in expandability, that is, a storage resource (e.g., an external storage apparatus) and a computer resource (e.g., a host) can be easily added, deleted, or replaced. A storage apparatus configured in the form of Redundant Arrays of Inexpensive Disks (RAID) is generally used as an external storage apparatus to be connected to the SAN. In this regard, a storage apparatus (also referred to simply as a storage) indicates a large-sized storage apparatus including disk devices and the like.
Recently, in association with expanded and complicated storage environments due to increase in data of firms and companies, there has been increasingly and widely employed “Thin Provisioning” which is a virtualizing technique of a storage system to simplify the operation and management of the storage system and to consolidate the storage environments.
The thin provisioning is a function to provide (present) a host with a thin provisioning volume for which the storage system has not a storage area (not corresponding to an actual area, i.e., an actual physical or logical storage area) to establish a correspondence between the thin provisioning volume and a set of virtual storage areas called a pool. When a host accesses the thin provisioning volume, the storage system allocates an actual storage area to an area of the thin provisioning volume.
For example, JP-A-2005-11316 describes a technique in which when a host carries out an operation to write data in a thin provisioning volume of a storage, an actual storage area is first allocated to an associated area of the thin provisioning volume. U.S. Pat. No. 6,823,442 describes a technique in which a thin provisioning volume to be accessed by a host is disposed in a storage system to allocate a physical storage area to the thin provisioning volume.
Since a plurality of thin provisioning volumes may correspond to one pool, the system is capable of effectively use virtual storage areas of the pool. Specifically, it is possible that the storage system beforehand arranges thin provisioning volumes virtually having a large capacity such that new virtual storage areas are added to the pool depending on the state of utilization of the pool to thereby increase the virtual storage capacity. On this occasion, it is not required in the initial stage to prepare or to arrange all hardware resources or storage media corresponding to the virtual storage areas, but it is only necessary to add such required hardware resources later according to necessity. This leads to, for example, an advantage that inexpensive hardware resources or storage media are later purchased for installation thereof according to necessity.